| abstract |
An oily lubricant for mixing with the refrigerant 1,1,1,2-tetrafluoroethane (R134a) is an ester of viscosity 2-30 mm²/s at 100°C. n Suitable classes of esters are (1) polyesters of a polyol and straight or branched chain carboxylic acid (CA), (2) diesters of neopentyl glycol and a C6-9 CA, (3) complex esters of partial esters of an aliphatic polyhydric alcohol with C3-C9 fatty acids and aliphatic or aromatic di CA, (4) C16-22 diallyl esters of aliphatic di- CA, (5) C18-26 diethyl esters of aromatic di-CA, and (6) diesters of an addition product of an alkylene oxide to a monohydric alcohol by an aliphatic di-CA. n The viscosity is adjusted by using mixture of esters or by adding a polymer; suitable viscosity for a refrigerator is 2-9 mm ²/s and for a car air conditioner it is 7-30 mm²/s. n The ester should be purified to have a low acid number of 0.1-0.5 mg KOH (g), to prevent metal corrosion, whilst keeping high insulating property, and it is purified so as to be stable and to have no more than 500 ppm of moisture. n An anti-wear agent of the sulfur type is preferably added in amount of 0.01-5 w/t%, and other additives can be an anti-oxidant and corrosion inhibitors. n The lubricant has excellent compatibility with R134a, low hygroscopicity, high thermal stability and lubricating property. |